1. Field of the Invention
The present invention relates to an attachment for a hand truck and, more particularly, to a stair climbing and descending attachment.
2. Description of the Prior Art
Climbing and descending stairs with a loaded hand truck presents a problem that those skilled in the art have long sought to solve satisfactorily.
One of the most common solutions uses a pair of endless belts that travel on pulleys secured to the truck. The endless belts comprise a kind of conveyor to support the truck on the edge of a stair. The worker moves the truck up or down the stairs by first supporting the truck on the edge of a stair on the belts. As he raises or lowers the truck, the belts travel around the pulleys and "convey" the truck relative to the stair. Variations of the endless belt "conveyor" concept are described in these U.S. Pats.: No. 2,467,644 to Wright et al.; No. 2,635,887 to Menne; No. 2,710,195 to Kurth; and No. 2,772,096 to Hanson.
However, none of those prior art solutions are wholly satisfactory. Perhaps their most serious defect is that they all use moving parts. Experience shows that any device having moving parts is more susceptible to breakage than a device without them. Furthermore, moving parts require bearings where they connect to stationary structure, and bearings require periodic lubrication. Thus, those prior art devices are more complex, more expensive to manufacture, and more expensive to maintain than would be the case if they used no moving parts.
U.S. Pat. No. 2,519,113 to Cohn and U.S. Pat. No. 3,788,659 to Allen reveal another approach to the problem. They disclose stationary runners which are secured to the truck. The runners support the truck on the edge of a stair and the truck slides up or down relative to the stair edge on the runners. That approach, however, creates problems, too, even though it eliminates the problems moving parts present. The surfaces of the runners that contact the stair edge are bare metal, which can severely damage unprotected stairs, particularly stairs that are carpeted.
The prior art, then, leaves much room for improvement in stair climbing and descending attachments for hand trucks.